IEEE - Aerospace and Electronic Systems - May 2021 - 34

Flight Demonstration of a Hybrid Battery/Supercapacitor Energy Storage System in an Earth Orbiting CubeSat

Figure 8.
Summary of hybrid battery model development. A-1) Equivalent circuit model on the operation of the hybrid energy storage system. The
supercapacitor impedance is described by RESR in series with Csc. A-2) The circuit model for performance characterization during extended
mission phase. The Ro is the electrolyte resistance. The charge-transfer time constant is associated with R1 and C1. The SEI time constant is
associated with R2 and C2. The diffusion time constant is associated with R3 and C3. B-1) Example of complex plane plot from EIS measurements for parameterization of impedance-based circuit model for Li-ion cell. A collection of EIS measurements were performed at various
SOC and temperatures. B-2) Each measurement fits sufficiently well to an impedance equivalent circuit containing R0 in series with three
-RC time constants. C-1) Simulation time profile of JPL/CSUNSat1 payload battery on discharge at T ¼ 5, 0, -5 C. C-2) Comparison of
simulation versus the telemetered discharge capacity profile. The simulation current rate was performed at 0.91 A.

with all three time constant variables as parameterized
by EIS measurements performed on the ground on the
same electrochemical cell chemistries using lookup
tables. The simulation of the discharge profile comparing JPL/CSUNSat1 telemetry is shown in Figure 8C-2.
The simulated discharge rate of 0.91 A represents the
average actual discharge rate through the 3.3 Ohm resistance in the electronic payload. The simulated temperature of -5 C to achieve minimum residual error is lower
than the actual payload battery temperature, which again
suggests significant ohmic resistances (i.e., leads, connectors, etc.) which are mostly present in the payload
assembly. These were unaccounted for from groundmeasured impedances from EIS on individual cells (see
Figure 8C-1). Overall, these data provided a good agreement with the model and basis for future improvements
on development of such circuit models, for flight operations on ESS life, and long-term state-of health
characterization.

SUMMARY
The JPL/CSUNSat1 project successfully demonstrated a
hybrid ESS consisting of a Li-ion battery and SC technologies in flight onboard a 2U tumbler CubeSat. Both the
primary and extended mission phases were completed successfully. The performance characteristics of the payload
34

hybrid ESS in flight were in excellent agreement with
ground test results, particularly with respect to the percent
of capacity contributions between the Li-ion cell and the
SC. The large differences in internal resistances from
flight experiments as compared to ground tests were attributable to significant ohmic resistances of the payload battery interconnects (i.e., leads, connectors, etc.) and not
due to the inherent cell impedances. Despite operating in
LEO, the spacecraft was able to achieve sub-zero temperatures critical for flight experiments on JPL's cold capable
hybrid ESS.

ACKNOWLEDGMENT
NASA's 2013 Small Spacecraft Technology Program
funded the payload development that was carried out at
the Jet Propulsion Laboratory, California Institute of
Technology, under a contract with the National Aeronautics and Space Administration and the CubeSat development carried out at the California State University,
Northridge. The JPL/CSUNSat1 primary operational
phase was funded by NASA's Center Innovation Fund.
The JPL/CSUNSat1 extended mission phase was funded
by JPL's Lunar Flashlight CubeSat Project. This work is
dedicated to the memory of Dr. Sharlene Katz, an exceptional educator and mentor to many students throughout
the CSUNSat1 project.

IEEE A&E SYSTEMS MAGAZINE

MAY 2021

IEEE - Aerospace and Electronic Systems - May 2021

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